Steam producing unit



Aug. 16, 1932.

c. B. GRADY 1,872,138

STEAM PRODUGING UNIT Filed Nov. 26, 1927 5 Sheets-Sheet 1 ,3,3, [l] :37a 4 MZK l f 35 INVENTOR A TT ORNE 15 Aug. 16, 1932. c. B. GRADY 1,872,138

` STEAM PRODUCING UNIT Filed Nov. 26, 1927 5 Sheets-Sheet 2 A TTORNEYJ Aug. 16, 1932. c. B. GRADY STEAM PRoDU'cING UNIT 1927 5 Sheets-Sheet 5 INVENTOR Filed Nov. 26

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STEAM PRoDucING UNIT Filed Nov. 26, 1927 5 Sheets-Sheet 5 Aug. 16, 1932.

m @di IN VENT 0R Bywz, 001025, wfwdf A TTORNEYJ nm@ @@@mmmm @m @@@m n `W l mg Patented Aug. 1,6, 1932 .UNITED STATESv PATENT OFFICE CHARLES B. GRADY, F WESTORANGE, NEW JERSEY, ASSIG-NOR TO METROPOLITAN ENGINEERING COMPANY, A CORPORATION OF NEW YORK STEAM PRODUCING UNIT Application led November 26, '1927. Serial No. 235,792.

Thisinvention relates to the generation of steam and is. concerned more particularly with a steam generating unit for heavy duty purposes, which may be used for the generation of steam at high and low pressures, superheated and reheated steam, and hot air, the unit containing control mechanism by which the temperature range of the superheated and reheated steam may be controlled. The novel unit is of utility for numerous purposes and may be used, for example, in industrial manufacturing plants, such as paper mills, where high pressure steam is desired for power, while low pressure steam and hot air may be used for.

` of the unit suitable for that purpose will therefore presently be described, this unit being tired with pulverized coal introduced vertically.

In a central power station built for very high eiciencies in accordance with present practice, the generating unit must be capable of supplying high pressure superheated steam at a pressure, for example, of

l 1400 pounds, for use in high pressure turbines. 'Low pressure turbines are also cuss tomarily employed, using high temperature superheated steam at a low pressure, for eX- ample, 400 pounds. The generating unit must therefore be capable of furnishing steam at these pressures and must include superheaters and also reheaters to raise the temperature of the steam passing from the high pressure turbines to the low pressure turbines. Such steam generating equipment must be flexible so that it can take care of normal loads efliciently and supply the de mand on peak loads or those yarising from emergencies. Ordinarily, in such a station, normal power loads are taken care of by the .high and low pressure turbines, the exhaust steam from the high pressure turbines being reheated and utilized in `low pressure turbines. Peak loads or those due to emergencies are then carried by additional low pressure turbines which are supplied with additional low pressure superheated steam which is generated in low pressure boilers which may also supply steam for heating and process work.

The present practice in the design .of steam generating apparatus for central station purposes involves the use of high pressure boilers which have a large amount of convection surface, together with superheaters and reheaters, and low pressure boilers which are also provided with superheaters. Such high pressure convection surface is costly to install and maintain.

The present invention is therefore directed to the provision of a steam generating unit to displace the apparatus above referred to, the new unit being of high capacity, compact design, and of relatively inexpensive construction. This apparatus provides steam for the various purposes mentioned above and the steam is generated at high efficiency. In addition, the invention includes a simple and positive method of controlling or regulating the temperature of superheated and reheated steam, heated in convection type superheaters and reheaters which are independent of the boiler heat-absorbing system and may be operated without affecting the heat transfer in that system to a substantial extent.

In the unit of the present invention, there is a boiler furnace which is especially suitable for pulverized fuel firing with turbulent combustion conditions, to produce a clear ame in the vicinity ofthe burners, with a simple arrangement of boiler heatabsorbing surfaces which have a large surface area exposed to the radiant heat of combustion. rlhese surfaces constitute a radiant heat boiler in which high heat transfer occurs, and

ing, resulting from variable operating conditions and accumulation of foreign matter on the tubesurfaces.

rIhe desirability of operating` at high uniform superheated steam temperatures is well understood. To accomplish this purpose, the control of temperature of the superheated and reheated steam provided for in the unit of my invention is in general effected by dividing the flow of the hot gaseous products of combustion leaving the combustion chamber, and causing variable quantities of these gases to flow immediately and without substantial loss in heat content to superheater and reheater surfaces, the remainder of the gases being directed in a separate and independent stream to convection surfaces. The quantity of gases flowing in the two streams is regulated and the flow in the stream passing to the superheater and reheater surfaces varies inversely in accordance with variations in the steam temperature. While the preferred embodiment of my invention'involves the use both of a superheater and a reheater, it is to be understood that the reheater may be omitted in specific installa- .tions wherein reheated steam is not required.

In one form of the unit a single combustion chamber is employed, provided with heat-absorbing surfaces constitutin a radiant heat boiler, and the gases flowing from the combustion chamber are divided into two separate streams leading to the superheater and convection boiler surface. Interposed between the combustion chamber and the convection surface is a supplementary furnace chamber provided with burners so that, in the event of peak or emergency loads, additional fuel may be introduced and consumed in this supplementary chamber to provide additional 'gases for heating the convection surfaces.

The principles of the invention may likewise be incorporated in a duplex unit if desired, in which there are two combustion chambers and two sets of convection boiler surface, a 'common superheater being used with or without a common:l 'reheater so that the independent streams of gases from the two units unite and flow as one through'thc superheater, and reheater, if the latter is used.

In each of these forms of the unit, a large heat transfer is accomplished in the combustionchamber by radiation from the flame and the incandescent solid particles, due to the favorable combustion conditions. Preferably the fuel is introduced into the combustion chamber in a vertically downward direction, and the independent streams flowing from the lower end of the latter turn back upon themselves and flow in opposite directions to the superheater and convection surfaces. During this reversal of flow, solid waste products or ash are precipitated and are deposited in a hopper bottom in the form of line particles.

By means of the unit above briefly described, I obtain a thermal eliciency equal to or greater than that secured in much more expensive and elaborate units of the construction now in use, thereby effecting a substantial saving in the cost of power, as well as obtaining safer, more reliable, and more economical operating conditions. This reduced cost of power is accomplished by the elimination of substantial amounts of costly high pressure convection surface, and reduced superheater and reheater surfaces, with the attendant reduced installation costs and fixed charges, and lower maintenance and operating cost.

For a better understanding of the invention, reference may be had to the accompanying drawings, in which Fig. 1 is a view in vertical section of one form of the apparatus,

Fig. 2 is a sectional view on the line 2 2 100 of Fig. 1,

Figs. 3, 4, and 5 are sectional views on the lines 3 3, 1-4, and 5 5 of Fig. l,

Fig. 6 is a view similar to Fig. 1 showing a duplex unit, and

Fig. 7 is a sectional view on the line 7 7 of Fig. 6, showing a detail of the construcion at different stages prior to its compleion.

Referring now to the drawings, the unit 110 illustrated in Fig. 1 includes a combustion chamber 10 elongated vertically and supplied with fuel through a plurality of burners 11 of any preferred type, for supplying a fuel-and-air mixture at the top of 115 the combustion chamber, through suitable openings in the refractory top wall 12. Duets 13 supply air for combustion'through openings in the top wall on either side of the. row of burners 11, these ducts receiving air 120 from blower 14 which has been heated by passage through the air heater 15. A part of the air from the heater l5 may be diverted through the passage 16, for supply to the line through which fuel is being in- 125 troduced to produce the fuel-and-air miX- ture, or for other purposes.

The vertical walls 17 of the combustion chamber are constructed of insulating material supported in any suitable manner, and 130 these walls are provided with heating surface in the form of tubes 18 lying side by side and extending vertically through the combustion chamber. The tubes on two of the side walls are connected at their upper Vends to drums 19 and 20, respectively, and

at their lower ends to drums 21 and 22, respectively. The banks of tubes on the other two side walls of the combustion chamber are connected at their upper ends to drums 23 and 24, respectively, these tubes extending downwardly beyond the drums 21 and 22 and being bent inwardly so that the tubes on both walls may be connected to a single lower drum 25. Alternate tubes in these opposite banks are bent sharply inwardly at the lower end of the combustion chamber, as indicated at 26, while the intervening tubes continue downwardly beyond the bottom of the combustion chamber walls and are given a similar bend at the point 27. Those portions of these tubes which lie beyond the lower end of the combustion chamber constitute water cooled openings through which the gases of combustion flow in passing from the combustion chamber.

At the lower end of the combustion chamber, the gases flowing therefrom are divided into two separate streams, one of which is diverted to the left, as illustrated in Fig. 1, through the passage 28, this stream thence flowing upwardly through the duct 29, in which superlieater surface is disposed. In the event that both superheater and reheater surfaces are used, the duct 29 is subdivided by a partition 30, as illustrated in Fig. 3, and the gases delivered from the combustion chamber through the passage 28 are subdivided and iiow in separate and independent streams past super-heater surface 31 and reheater surface 32. Beyond these surfaces, the gases pass through the air heater 15, in which are placed a. plurality of parallel air passages 33, through which the air from the blower 14 Hows in indirect contact with the gases in the form of a plurality of thin flat streams having a large surface exposed to the gases. Beyond the air heater, dampers 34 and 35 are provided, by which the amount of gases flowing through the superheater and reheater may be controlled. The use of the air -heater at this point accomplishes the two purposes of increasing the thermal efficiency of the installation and also of affording ease in regulation of the superheating and reheating action by control mechanism which is of inexpensive construction and easy operation. The placing of the dampers beyond the air heater insures that the dampers are subjected to the heated gases at a relatively lowtemperature due to heat extraction in the superheater, reheater, and air heater. In the! event that the reheater is not employed, the partition 30 may be dispensed with and only a single .damper used.

Another portion of the gases leaving the combustion chamber 10 flows through the water cooled openings provided by the tubes 18, and then turns in'to the chamber 36, whence the gases pass between tubes 37, constituting other water cooled openings, and into chamber 38, which may be designated a supplementary combustion chamber. The tubes 37 extend from a header 39 at the top of this combustion chamber, down along the insulating wall 40, protecting that wall, thence across the passage 36 to the header 37A. Beyond the combustion chamber 38 in the direction of flow of the gases are banks of tubes 41, 42, provided with the usual baiiies 43, these banks of tubes constituting convection boiler surface. vWhile this surface may be arranged in any convenient manner, as illustrated, the tubes in bank 41 lead from a lower drum 44 to an upper drum 45 connected by a bank of tubes 46 to a drum 47, which is in turn connected by the tubes of bank 42 to the drum 44. The gases flow through these banks of tubes in the usual manner and are then led to a flue 48, in which there may be placed a damper, similar in construction to the dampers 34 and 35, which may be preceded by an air heater or economizer of standard construction (not shown). The dampers make it possible to control the quantities of gases which flow in the independent streams through the convection surface and the superheater and reheater sur; faces either manually or by some standard thermostatic means which actuates the dampers to regulate the exit temperatures of the superheated and reheated steam.

Through the upper refractory wall 49, of the supplementary combustion chamber 38 fuel may be introduced for combustion in this chamber to take care of peak and emergency loads, through a battery of burners 50, air being supplied through the ducts 51 and 52. With this arrangement, the stream of gases from the main combustion chamber is subdivided into two independent streams, one of these streams passing directly to superheater surface, and the other to convection boiler surface. Radiant heat is absorbed in the main combustion chamber by the tubes 18,

while if the supplementary burners are being fired, radiant heat from combustion chamber 38 is absorbed by a portion of the tubes of the bank 41 and by the tubes 37. One of the streams of gases from the radiant heat boiler is further subdivided, in the event that reheaters are used, but the superheaters and reheaters receive gases direct from the combustion chamber which have not given up heat to convection surface.

From each end of the drum 23 a pipe 53 leads to a T 54, connected by pipe 55 to the drum 25, this drum being placed beneath rey circulatory piping, constitute a convection' fractory bottom 56 of theV furnace, which is arranged to form the hopper bottoms 57 and 58. A pipe 59 connects. each T 54 with one end of the drum 24, and a branch`pipe 60 connects one pipe 59 with drum 22. Similarly, a branch pipe 61 connects one pipe 59 to drum 20, and drum 19 is connected by branch pipe 62 to the pipe 53, and drum 21 is connected' by pipe 63 to pipe 53. The connections are duplicated, though reversed, at opposite ends of the chamber 10, so that the drums 19-4-25 are connected together.

The drums 19, 20, 23, and 24 are connected to the header 64 of the superheater by two pipes'65 and 66, leading to a T 67, the pipe 65 being connected to the drums 19 and 23 while pipe 66 is connected to drums 20 and 24. The T 67 is connected to header 64 by a pipe 68. The header 64 is connected to the superheater tubes 31, the eXit ends of these tubes leading to a header 69 connected by a pipe 70 to the apparatus in which the superheated steam is to be utilized.

The drum 37A to which the tubes 3700nnect is connected by a pipe 71 t'o the drum 45 which is connected to the drum 47 by the bank of tubes 46. The drum 47 is connected by a. pipe 72 to the header 7 3 connected to reheater tubes 32, and these tubes are connected at their other ends to t-he header 74, provided with a pipe 75 leading to the apparatus where the reheated steam is to be utilized. A connection 72 to pipe 72 may be used for leading exhaust steam to the reheater along with steam'from the drum 47 or if desired, any other suitable connection may be used for the purpose. vSuitable feed Water supply connections (not shown) are also provided.

The drums 19, 20, 21, 22, 23, 24, and 25, with the plurality of water wall tubes lining the combustion chamber 10, together with the circulatory piping, constitute a radiant heat boiler, as the steam generated will be largely by radiation and Very little by convection. The drums 44, 45, and 47, together with the connecting tube banks 41 and 42, the water wall tubes 37,'drums 39 and 37A, and the boiler as the steam generated will be largely by convection and very little by radiation when the unit is operating at normal loads without burners 50.

If desired, the tubes 18 may be protectednear their upper ends as indicated at 10 by refractory material, such as the carborundum blocks illustrated in my copending application, Ser. No. 174,315, filed March l0, 192

In Fig. 6 there is shown a duplex unit embodying the principles of the present invention, this unit having two combustion chambers with radiant heat surface, two sets of convection boiler surface, and a common superheater with or without a common reheater.

One wall of the combustion chamber 76 is f provided with a bank of tubes 81 leading from a drum 82 to aV drum 83. The tubes I in the bank 81 are placed side by side and serve as a defining wall for the chamber. Alternate tubes of the bank 81 are connected to a drum 83 at different points so that at the point indicated at 84 the tubes are separated and permit gases to ow between them, thus forming water cooled outlets. Opposite the bank of tubes 81 is a row of tubes 85 forming part of a bank of tubes 86, leading from the drum 87 to t-he drum 88. Another bank of tubes 89 ,leads from the drum 88 to an upper drum 90, which is connected by a bank of tubes 91 to the drum 87, suitable baliles 92 being provided to direct the gasesy through the, banks of tubes 86 and 89 in a circuitous path. From the bank of tubes 89 the gases pass into an outlet duct 93 leading to an air heater 94, simil'ar in construction to the air heater 15, a dam er 95 being provided in the duct beyond connected to the drum 83 leads to a drum connected by a pipe 101 to the drum 82,

t air-l. heater. The drum 83 lies beneath refradtofy' iioor material 96 arranged to form hopper bottoms 97 and 98, anda screen of tubes 99 the tubes 99 forming a protective screen for;

the hopper bottom 97, to prevent the fusion' of ash which may collect in the hopper boty tom 97.

The combustion chamber 77 is provided a bank of tubes 86. Another bank of tubes 89 leads from the drum 88 to the drum 90. which is connected by tubes 91 to the drum 87. The gases flowing through the banks of tubes 86 and 89 are directed by baffles 92 into a duct 93 in which is placed an air heater 94 and a damper 95.

The banks of tubes 81 and 81 with the side walls of the furnace define a passage 102 in which is placed superheater surface in the form of tubes 103. Reheater surface may also be placed in this passage 102, in which event the passage will be subdivided by a partition similar to that ,illustrated at 30 in Fig. 3. Beyond the superheater and rehcater tubes, if the latter are used, the hot gases flow through an economizer of standard construction, beyond which a damper 34' is provided with or without a second damper 35', depending on whether a reheater is used. In the passage 102, between tubes 103 and the economizer 110 is located emergency high heat limit device 112', situated for the purpose as heretofore described relative to Fig. 1.

The tubes 81 and 81 are placed side by side and in order to prevent gas leakage through them which would short circuit the gas flow, the spaces between the tubes are sealed for a portion of their length in the manner illustrated in Fig. 7. At intervals along this portion of the tubes short wires 104 are spot welded, or otherwise fastened tothe tube, these wires being placed on adjacent tubes so as to extend across each other. A wire 105 is then placed' in the angle between Wires 104, and near each pair of wires 104 is placed a staple 106, the legs of these staples straddling the wire 105. The extending legs of the staples and projecting ends of the wires 104 are then twisted together, as

indicated at 107, and suitable heat-resistant material, such as asbestos, is forced between the tubes, as indicated at 108. The wires are then protected by a strip or mass of plastic material 109, placed in the bight of the tubes. This arrangement seals the tubes for this portion of their length so as to forma substantially gas-tight wall, the sealing extending a considerable distance down the tubes so that the gases flowing from the combustion chamber will have to pass downwardly a substantial distance before they can flow between the tubes and into the passage 102.

With this arrangement it will be seen that,

due to combustion of fuel in the chamber 76,

radiant heat will be absorbed in the tubes 81 and 85, while the gases will flow downwardly through the combustion chamber, and near the lower end thereof will be subdivided, part of the gases flowing back upon themselves and up through the bank of tubes 86, the tubes 89, and thence out through duct 93. Another portion of the gases will flow through the water cooled openings between tubes 81, near the point 84, and then turn back upon themselves and flow upwardly in passage 102 through the superheater and reheater, if the latter is used. In the combustion chamber 77 the same subdivision of the gases occurs,

. part of the gases flowing through banks of tubes 86' and 89', while another portion of the gases flows in a separate and independent stream into passage 102, where it mingles with the stream from the chamber 76, and the combined stream flows through the superheater and reheater surfaces.

The gases of combustion give up heat first to radiant heat surface, represented by the tubes 81, 85, 81', 85', 99, and 99', then are subdivided and flow to convection surface, represented by the main portion of the tubes in the banks 86 and86' and the tubes in banks 89 and 89'. From each combustion chamber the gases flow to the superheater and reheater surfaces in streams which are entirely separate and independent from those flowing through the convection surfaces. The extent of gas flow through the convection surfaces and through the superheater and reheater surfaces may be controlled by means of the dampers, so that a greater or less amount of gases may flow in these several streams in accordance with requirements on different occasions.

Tubes 81 and 81 act as a defining wall of combustion chambers 76 and 77. The side walls of these chambers may be of refractory material, or these side walls may carry additional rows of tubes connected into the vradiant circulatory system.

The drums 82, 82', 83, 83', 100 and 100', together with the water wall tubes 81 and 81', the water screen tubes 99 and 99', and the circulatory piping constitute two radiant heat'boilers, as the steam generated will be largely by radiation and only to a slight extent by convection. Drums 87, 87', 88, 88', 90, and 90', together with the tube banks 86, 86', 89, and 89', constitute a convection boiler,

as the steam generated will be largely by conl vection and only to a slight extent by radiation.

This duplex unit is well adapted for a large size single pressure unit, say 400 pounds to 600 pounds pressure. The six drums, two on the radiant heat boilers and four on the convection boilers, provide large steam releasing surface, and with the division and diversion of the gases, the arrangement of the convection surfaces in three divisions, twoboiler and air heater divisions, and one superheater and economizer, or superheater, reheater, and economizer division, makes possible the construction of a unit to produce steam in hourly quantities of the order of twice those produced in any unit of which I am now aware.

These portional divisions, utilizing hot gases coming from a combustion chamber having a substantial amount of water cooled surface, effect a great saving in convection surface, as they give higher temperature differences and higher gas flows per square foot per pound per degree temperature difference per hour. These surfaces, therefore, may be used with the same or higher efficiencies, and the same or even less draft loss than the units now in use.

In the apparatus illustrated in Fig. 1, the radiantheat boiler if desired may be for high pressure steam generation at a pressure, for example, of 1400 pounds, and the convection boiler may be for low pressure steam generation, for example at 400 to 600 pounds.

Vhile the arrangement above mentioned is 5 I claim:

1. A steam generating unit comprising the combination of a combustion. chamber and a burner for introducing fuel for combustion therein, radiant heat boiler surface on the walls of the combustion chamber for absorbing radiant heat in substantial amounts, an independent boiler made up substantially entirely of convection surface, a superheater, an outlet from the combustion chamber disposed beyond the radiant'heat surface in the direction of iiow of the gases, and means for subdividing the gases flowing through said outlet and leading the gases in separate and independent streams to the superheater and independent boiler respectively, the said means affording control of the quantities of gases in the two streams.

2. A steam generating unit comprising the combination of a combustion chamber and a burner for introducing fuel for combustion therein, radiant heat boiler surface on the walls of the combustion chamber for absorbing radiant heat in substantial amounts, a convection boiler independent of said radiant heat boiler disposed outside said combustion chamber, a superheater, and means for subdividing the gases flowing from said radiant heat boiler and leading these gases in separate and independent streams to the superheater and convection boiler respectively.

3. A steam generating unit comprising the combination of a radiant heat boiler including heat-absorbing elements defining a chamber having an outlet, an independent convectionboiler, a superheater, means for supplying fuel for combustion in said chamber, the burning' fuel giving up radiant heat to said radiant heat boiler, and means for leadingl the gases from said radiant heat boiler to the convection boiler and the superheater in separate and independent streams.

4. A steam generating unit comprising the combination of a radiant heat boiler including heat-absorbing elements defining a combustion chamber, an independent convection boiler, a superheater, means for supplying fuel for combustion in said chamber, the

burning gases giving up radiant heat to said heat-absorbing elements of the radiant heat boiler, means for leading the gases from said radiant heat boiler in separate and independent streams to the convection boiler and the superheater, and means for passing air in heat exchange relationship with the gases flowing from said superheater to extract heat therefrom.

5. A steam generating unit comprising the combination of a radiant heat boiler including heat-absorbing elements defining a combustion chamber, an independent convection boiler, a superheater, means for supplying fuel for combustion in said chamber, the hot gases giving up radiant heat to the heatabsorbing elements `of said radiant heat boiler, means for leading the gases from said radiant heat boiler 1n separate and independent streams to the convection boiler and dependent convection boiler, a superheater, a n

reheater for steam, means for burning fuel to give up radiant heat to said radiant heat boiler, means for leading a portion of the gases from the radiant heat boiler in a stream to the convection boiler and for leading the remainder of the gases in two streams sep- 'arate and independent from each other and from the first to the superheater and reheater respectively, means for heating air by passing the air in heat exchange relationship with the gases flowing from the superheater and reheater, and control means for controlling the quantities of gases in the three streams, the said control means being in part disposed beyond said air heater in the direction of gas flow. v

7 A steam generating unit comprising the combination of a radiant heat boiler including heat-absorbing elements defining a combustion chamber, a convection boiler, a convection superheater connected to the radiant heat boiler to receive steam therefrom, a second superheater connected to the convection boiler to receive steam therefrom, means for burning fuel in said chamber, the hot burning gases giving up heat to the heat-absorbing elements of the radiant heat boiler, and means for leading the gases of combustion from the radiant heat boiler in separate and independent streams, one flowing to the convection boiler and the other to the superheater and said second superheater.

8. A steam generating unit comprising the combination of a combustion chamber and a burner for introducing fuel vertically downwardly into the chamber for combustion in suspension therein, heat-absorbing surface on the walls of said chamber constituting a radiant heat boiler, convection boiler surface outside said chamber and independent of said radiant heat boiler, a superheater outside said chamber, and means for leading the products of combustion from said radiant heat boiler in two separate and independent streams which change direction in passing to the con` vection boiler surface and to the superheater respectively.

9. A steam generating unit comprising the combination of a radiant heat boiler, a convection boiler independent thereof, a super-` heater, means for burning fuel in the radiant heat boiler to give up radiant heat to the surfaces thereof, means for leading the products of combustion from the radiant heat boiler in two separate and independent streams to the convection boiler and the superheater respectively, and means for burning fuel and lead- 'ing the products of combustion to said convection boiler, the said means being independent of the means for burning fuel in the radiant heat boiler.

10. A steam generating unit comprising the combination of a radiant heat boiler, a convection boiler independent thereof, a superheater, means for burning fuel in the radiant heat boiler to give up radiant heat to the surfaces thereof, means for leading the products of combustion from the radiant heat boiler in two separate and independent streams to the convection boiler and the superheater respectively, and means for burning fuel outside said combustion chamber and .leading the products of combustion thereto the surfaces thereof, means for leading the products of combustion from the radiant heat boiler in two separate and independent streams to the convection boiler and the superheater respectively, a supplementary combustion chamber, and means, for burning fuel in said supplementary combustion chamber and leading the products of ,combustion to said convection boiler.A

12. A steam generating unit comprising the combination of a radiant heat boiler, a convection boiler independent thereof, a superheater, means for burning fuel in the radiant heat boiler to give up radiant heat to the surfaces thereof, means for leading the products of combustion from the radiant heat boiler in two separate and independent streams to the convection boiler and the superheater respectively, a supplementary combustion chamber through which the stream of gases to said convection boiler flows, and means for supplying fuel for combustion in said supplementary combustion chamber, the gases of combustion {iowing with the gases from said radiant heat boiler to the convection boiler. A

13. A steam generating unit comprising the combination of a radiant heat boiler, a convection boiler independent thereof, a superheater, means for burning fuel in the radiant heat boiler to give up radiant heat to the surfaces thereof, means for leading the pro-ducts' of combustion from the radiant heat boiler in two separate and independent streams to the convection boiler and the superheater respectively, a supplementary combustion chamber, means for burning fuel therein and leading the products of combustion to said convection boiler, and heatabsorbing surface connected to said convection boiler for abstracting radiant heat from the combustion taking place in said supplementary combustion chamber.

1l. A steam generating unit which comprises the combination of a combustion chamber having radiating refractory sur# face forming a part of the vdefining wall thereof, radiant heat absorbing surface along the walls of the combustion chamber, a superheater, a convection boiler independent of said radiant heat-absorbing surface, means for introducing fuel into the chamber for ignition by heat radiated from said refractory surface and combustion within said chamber, and means for leading the products of combustion from said chamber in separate and independent streams to the superheaterand the convection boiler.

15. In a steam generating unit, the combination of a' combustion chamber, heat-absorbing elements along the walls only of said chamber, means for introducing fuel for combustion' in said chamber, an adjacent chamber, a superheater therein, and a delining wall for the combustion chamber having water-cooled openings therein forming an outlet from the combustion chamber to the adjacent chamber.

16. A steam generating unit which comprises a vertically elongated combustion chamber, refractory material in the-said comi bustion chamber near the top thereof forming an ignition wall, radiant heat-absorbing surface forming part of the defining walls of the chamber, means for introducing fuel and air into the top of the chamber for ignition and combustion therein, an outlet from the bottom of the chamber, a superheater, a convection boiler outside the chamber and independent of the radiant heat-absorbing surface therein, and means for leading the products of combustion passing through the outlet to the superheater and to the reheater in se arate and independent streams.

n testimony whereof I aiiiX my signature.

CHARLES B. GRADY. 

